13 in our house to get your first cheap, refurbed smartphone. We make a huge deal of it. They get the following as gifts on their 13th bday: state ID card, phone, a new wallet, a bus pass, and we open a checking account for them (except for younger, he had to wait until 14 due to new credit union rules). They become "young adults" in our home at 13, and we build up to this big time. It comes with privileges and a ton more responsibilities, but they are now junior adults in the household and they are treated as thus. If they keep their phone in pristine condition and have no usage issues, they can get a newer, more capable one at 15 in lieu of a birthday gift. We have few internet restrictions or rules. Just lots and lots of family discussions and education. I have one adult son that's about to head off to his junior year of college, and one teenager still at home. Never had any issues with bullying or other stuff. Some gaming issues with older son, but we taught him methods to control his own behavior rather than implementing restrictions that would have controlled it for him.
But then, I've been informed we do the parenting thing all wrong, so ::shrug:: We don't punish teens for misbehavior, for example. If they misuse their phone or the internet, they have already punished themselves. Since they knew there were no parent-induced repercussions, they were always honest and came to us when they made a mistake and got in over their heads, and then we could help them work through it. BUT there's no one right answer. Know yourself, know your kid, and do what's best for your family. Don't look to other families for a solution. They have a totally different dynamic. The dynamic that worked for our boys was likely set into motion at birth simply due to our innate parenting style and their personality types, it may not work for someone else.